This invention relates generally to ultrasonic transducers and more particularly to ultrasonic surface acoustic wave transducers.
The use of pulse-echo ultrasonic nondestructive test methods to inspect workpieces, for example gas turbine engine components, for flaws or defects is known in the prior art. When testing workpieces by the pulse-echo ultrasonic test method, the workpiece and the transducer are typically immersed in a liquid coupling medium, such as water, for achieving good ultrasonic coupling. A transducer, for example a surface acoustic wave (SAW) transducer, produces surface waves in a target material by converting input radio frequency (RF) electric signals into acoustic waves which are directed at the workpiece, where they form surface acoustic waves. The surface waves travel along the surface of the target material and are eventually re-radiated back through the coupling medium to the SAW transducer which reconverts the acoustic waves back into output RF electric signals. The pattern of the output signals can be used to determine the presence of defects on the surface of the workpiece.
Commercially available SAW transducers are typically of hemispherical form and tend to radiate direct reflective waves in addition to surface waves. These direct reflective waves can contaminate the inspection results. These disadvantages may be ameliorated by the use of multiple transducers or phased-array transducers, however these options increase the expense of the transducers and related equipment and also complicate the transducer set-up and inspection processes.
Accordingly, there is a need for a simple SAW transducer which reduces contamination of inspection results.